I am considering 245/40/18 on my 9.5 and 265/40/18 on 10.5 but I have a few questions. You have a lot of experience with tyres and wheel, so I want to ask you these.

1. How does a stretched tyre (245 on a 9.5 for example) affects performance and handling generally. Particularly in high speed cornering?
* to make it easier for me to understand, lets go extreme a lil. Lets say I put a 225 on a 9.5 and stretch it, how does this effect performance particularly high speed cornering?

2. What difference will it be for rubbing issues when say using 245 on a 9.5" vs 245 on a 9"?. Will the most upper part of the tyre be equal to as if I put it on a 9"?
Let me make myself more clear, lets say I use a 245 on a 9 inch wheel and 245 on a 9.5 wheels inch, the rubbing issues will be similar or has a lot of difference?

Thanks a ton for your time here.
Razif

Razif,
If these wheels are specifically designed for the M3 and they are not fitting correctly, I would first check with the manufacturer of wheel to see what size they recommend for their wheel. They should know exactly what tire size is best for their wheel if the wheel was designed to be used on the M3.

1. 245/40/18 is the narrowest we would recommend on a 9.5" width wheel. The rim edge will poke out a little, but it would not be consider stretched because it is withing the rim width range of the tire. 245/40/18 has a rim width range of 8.0-9.5". Using 245/40/18 on a 9.5" width rim will cause the sidewall to flex very little under corning, this will make the turn in feel extremely precise.
225 would be stretched and would be unsafe. Stretching a tire beyond it's designed rim width will add stress to the sidewall and the bead of the tire. Using anything smaller than 245, you run the risk of the tire coming off the wheel.

2. Rubbing would be less on a 9" than the 9.5"... But that's dependent on the exact tire and wheel and offset being used. If all things are equal, then one would expect rubbing to be less on a 9".

If you have any further questions, please email me directly.
Thank you.

When will Tire Rack be getting in your inventory of Winter Tires for our M3s? Specifically, I want to put winters on my 19" OEM style 359 zcps. What will be available and when (Michelin Alpin 4s, Blizzak LM-001s, etc.)? And what sizes do you recommend OEM 245/265 or minus 1 235/255? Please do not suggest going to 18" because I have a BBK which will not accommodate 18" wheels so I am stuck using my 19" wheels.